1. Field of the Invention
This invention relates to a single-lens reflex camera with a display for displaying information of various kinds within the view finder of the camera, and particularly to a single-lens reflex camera arranged to display letters, patterns, etc. by means of a liquid crystal within or outside the visual field frame of a view finder.
2. Description of the Prior Art
Heretofore various view finder display devices have been proposed for single-lens reflex cameras such proposals include devices of the type arranged to display photographic information with a liquid crystal outside of the visual field frame of a view finder. Another type uses a liquid crystal disposed covering the optical path of a view finder and arranged to superimpose letters, patterns, etc. on the view field. The liquid crystals are of the light transmission type. In many cases, T.N. cells, etc., that utilize the torsional effect of a nematic liquid crystal have been employed for this purpose. In addition, it has recently become known that a G.H. liquid crystal which as a guest-hose effect is also usable for displays. Such a crystal uses various kinds of dyestuff molecules as guest and liquid crystal molecules as host to obtain the rotatory orientation of the dyestuff molecules.
In displaying various kinds of information in a pattern within the view finder of a camera using a T.N. liquid crystal plate or a G.H. liquid crystal plate, a portion of the display pattern maybe located within the visual field frame of the view finder and a portion of the display pattern maybe located outside of the visual field frame are both arranged for display by a single liquid crystal plate. In that case the portion of the display pattern located outside the visual field frame must have a high contrast while the portion which is located within the visual field frame and which is a superimposed display does not have to have a high contrast. In view of this, the liquid crystal display plate must be arranged to meet this requirement. Assuming that a display is to be placed within a view finder, such as mentioned, using a guest-host type liquid crystal, an ordinary polarizing plate must be used for obtaining the sufficient contrast required for the display portion outside of the visual field frame even with a G.H. type liquid crystal. Using the polarizing plate results in obtaining only 50% of the oncoming light even if the polarizing plate is ideal. This inevitably darkens the visual field of the view finder. If a G.H. liquid crystal plate is used alone without the polarizing plate to avoid this lightless, the display portion outside the visual field frame is not readily visible due to the insufficient contrast although the display portion within the frame may be readily visible.
Further, in a electric light shielding element. This is for the following reason. If the light reaches the light shielding element before it passes to the light measuring element, the quantity of light received at the light measuring element when information is displayed by the photo-electric light shielding element differs from the quantity of light received when no information is displayed by the light shielding element. To avoid such variation in the quantity of light, light has heretofore been guided to the light measuring element in the following manner:
(1) A half-mirror is arranged in front of the photo-electric light shielding element to guide the light flux to the light measuring element.
(2) A half-mirror is disposed at the 45.degree. mirror and the light flux is guided through the sub-mirror to the light measuring element.
The above conventional arrangement, however has the following shortcomings:
(1) It is impossible to measure the light after the light has passed through the photo-electric light shielding element. Therefore, the arrangement allows little latitude in determining the position of the light measuring element. It has been thus impossible to perform a light measurement at the pentagonal optical system of a camera. In the case of a camera of the type having an in-focus detector and capable of automatic focusing to effect an in-focus display, an in-focus detecting element is often disposed below a 45.degree. reflecting mirror. In such a case, the positional restriction imposed on the arrangement of the light measuring element becomes more severe.
(2) Since the light flux is guided to the light measuring element before it is guided to the view finder optical system, the view finder is always dark.
To eliminate the disadvantages, it is possible to perform the light measurement and the display in a time sharing manner by means of a timing signal and to arrange the photo-electric light shielding element at a stage preceding the light measuring element. However, where a slow responsive photo-electric light shielding element such as a liquid crystal (LC) or an electro-chloric cell (EC) is used in such an arrangement, the time sharing period inevitably becomes long and results in undesirable flickering of the displayed information.